[Sidefx-houdini-list] alpha for particles in mantra?

François Duchesneau sidefx at trinix.ca
Sun Jul 20 19:33:53 EDT 2008

I think the Vex Decal doesn't deal with the alpha. Try the Vex Layered 
Surface and I think you've got to change the "Texture Hint" to "Diff + 
Alpha", something like that.


Michael O'Brien wrote:
> Hola~
> Following the directions on the sidefx website, I was able to get a disk
> sprite displayed in the OpenGL viewport that correctly responds to color and
> alpha in GL. I created a VEX decal and a Mantra Sprite Procedural that are
> read by the sprite pop.
> However, when I go to render them, alpha isn't used. I'm new to the VEX
> language, so I might be just missing something obvious, but it looks like
> alpha isn't accounted for in the decal code. Is that right? Sometimes I look
> at VEX and try to read it as SL, which might be getting in the way.
> The particles have an alpha property. I setup pscale and all the mantra
> knobs I can find to accommodate rendering transparent disks. The color works
> fine, but the alpha doesn't. Any help would be appreciated.
> One thing I find interesting is that in the FX Tools both wispy smoke and
> heavy smoke have rough geometric cages with shading applied to make it look
> like smoke. At Pixar, we would render heavy smoke using a volumetric
> approach and wispy smoke as using a ton of nearly transparent particles as
> disks. Do people render large numbers of transparent disks in Mantra? In
> other words, is it that my approach is wrong?
> MO
> --
> Michael K O'Brien                               Production Engineering
> Pixar                                                mobrien at pixar.com
> REMY: What is that?
> EMILE: I don't really know.
> REMY: You don't know... and you're eating it.
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